NMR Speciation of Aqueous MAPA, Tertiary Amines, and Their Blends in the Presence of CO₂: Influence of pK_a and Reaction Mechanisms

Abstract

The diamine 3-(Methylamino)propylamine (MAPA) and eight tertiary amines were studied as single and blended aqueous CO2 absorbents at different concentrations and ratios to investigate the reaction mechanisms. After absorption (40 °C) and desorption (80 °C) experiments, quantitative 13 C NMR experiments were performed on each liquid sample.After absorption, the following CO2-derived species were identified and quantified:(bi)carbonate in each amine system; primary and secondary MAPA carbamate, and MAPA dicarbamate in MAPA-systems; tertiary amine carbonate in tertiary amine-systems.Concerning desorption, the main CO2-species removed was (bi)carbonate, followed in the blends by MAPA dicarbamate.Since, after CO2 absorption, the concentration of MAPA dicarbamate was negligible in single MAPA and, in the blends, mainly increased at increasing pKa of the tertiary amines, it is concluded that the tertiary amines increase the availability of MAPA species to react further with CO2. MAPA and tertiary amines appear to influence each other also for the CO2 release.

Vapour-liquid equilibrium study of tertiary amines, single and in blend with 3-(methylamino)propylamine, for post-combustion CO2 capture

“…11). Similarly to other MAPA-tertiary amine blends [41], the species identified and quantified at equilibrium were MAPA/MAPA(H + )2, primary MAPA carbamate (MAPA(H + )COO(p)), secondary MAPA carbamate (MAPA(H + )COO(s)) and MAPA di-carbamate (MAPA(COO )2), tertiary amine, tertiary amino carbonate and (bi)carbonate (HCO3 / (2HE)PRLD blended with MAPA was 14.4%, 11.2% and 11.4%, CO 2 ). In Fig.…”

“…Liquid samples collected from the low-pressure VLE apparatus were examined by means of NMR spectroscopy to characterise the species at equilibrium. In particular, the species concentrations were measured by acquiring quantitative 13 C NMR experiments at T = 300.0 K on a Bruker 600 MHz Avance III HD instrument equipped with a 5-mm cryogenic CP-TCI z-gradient probe, using the same method as described in Perinu et al [41].…”

“…Speciation data in blended MAPA solutions. (a) MAPA-CO2 derivative species; (b) (bi)carbonate; red, 3 mol/dm 3 3DMA1P + 1 mol/dm 3 MAPA; black, 3 mol/dm 3 1-(2HE)PRLD + 1 mol/dm 3 MAPA; blue, 3 mol/dm 3 3DEA1P + 1 mol/dm 3 MAPA reported in Perinu et al[41]; green, 3 mol/dm 3 DEEA + 1 mol/dm3 MAPA reported in Perinu et al [41]; (D) MAPA(H + )COO (p), (s) MAPA(H + )COO (s); (h) MAPA(COO )2; ( ) HCO3 /CO 2 . (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.…”

Aqueous MAPA, DEEA, and Their Blend as CO2 Absorbents: Interrelationship between NMR Speciation, pH, and Heat of Absorption Data

“…Tertiary amines cannot react with CO2 directly, although a limited number of authors have observed the formation of alkyl carbonate in aqueous tertiary alkanolamines. 11,[20][21][22][23] Jørgensen and Faurholt 20 suggested the reaction (2) in basic aqueous solutions of amino alcohols, and proposed the overall reaction (3) (which represents the inverse of the alkyl carbonate hydrolysis) as they observed the formation of the alkyl carbonate when mixing amines, bicarbonate and carbonate.…”

CO2 capture using highly viscous amine blends in non-porous membrane contactors

“…In particular, blends containing 3-(methylamino)propylamine (MAPA) and tertiary amines (referred also as third generation solvents) showed much better performance compared to traditional MEA-based solvents, both in terms of cyclic capacity and regeneration energy requirements [12,13]. The chemical mechanism involved behind the CO 2 absorption in this type of blended systems has been thoroughly characterized by Perinu et al [14]. Knuutila et al [15] reported 3 blends of MAPA with different tertiary amines (diethylethanolamine, DEEA; 1-(2hydroxyethyl)pyrrolidine, HEPP; 3-(diethylamino)-1,2-propanediol, DEA-PD) showing 30% lower reboiler duties (2.5 -2.6 MJ/kg CO 2 ) and 50% higher cyclic capacity than 30 wt% MEA.…”